"massacre" Q..to joe

[rx5]

Joe,


how did you get the 3.9K value?? did you also bias the DRAIN leg to 4.5VDC??

can I use P-type Power mosfet (IRF9530) in place of BS250??


thanks.... :wink:

-RaLPH

[Joe Davisson]

By the way, I yanked that schematic for favor of this:
http://www.joefus.com/pedals/images/obsidian.gif

It was just too similar, and the 100k gain control seems to match better than the 1M I used on the old Obsidian.

Anyway, the BS250's are "enhancement-mode", and I'm not sure power MOSFET's would work or sound right, at least not without changine values. The right transistors are available from Mouser for pretty cheap.

The 3.9k drain resistor puts the drain in the ballpark of 4.5 volts. For the MOSFET to work, the gate must be a certain level over the source (about 1.5v), then the drain resistor is chosen to set the operating point (optimally 4.5v).
-Joe

[rx5]

ok.... that seems to clear up.... so I bias the Gate to 1.5V and the Drain to 4.5V..... Gonna try the Power mosfet anyway.... but very expensive..  :?  2 dollars a piece for that IRF9530.... just gonna do a 1 stage only..... to see if it outputs "something"....



-thanks...




Ralph